Balb/c H-2db spleen cells generated a strong primary in vitro CML response against Balb/c (H-2)d wild type spleen cells. The effector cells generated were specific for L antigens. In an allogeneic CML response between two non-mutant strains directed against H-2D region antigens, two clones of cytotoxic effector cells could be identified, one with specificity for D antigens, and the second with specificity directed against L antigens. When syngeneic cytotoxic effector cells were generated against TNP modified H-2D antigens, no clones with specificity for L-TNP modified antigens could be detected. This contrasts with the H-2 restricted murine influenza model, in which influenza virus can be recongnized by cytotoxic T cells in association with products of the L locus. Therefore, although products of the L locus are capable of inducing allogeneic cytotoxic effector cells, and serve as self recognition structures for influenza virus, these antigens appear not to be capable of eliciting syngeneic effector cells specific for the TNP hapten.